1. Field of the Invention
The present invention relates generally to float assemblies for sensing fluid levels and, more particularly, to a float assembly for actuating a switch.
2. Background Art
Conventional float assemblies for actuating a switch based on a fluid level typically include a pushrod that extends upwardly from a float and which moves vertically with the float in response to changes in the fluid level. The pushrod may actuate the switch directly or, alternatively, may actuate the switch via an intermediate lever.
In applications where the float assembly controls the operation of a pump, it is desirable to provide switching hysteresis or a control deadband that allows the pump motor to cycle between on and off operational states at an acceptable frequency and duty cycle. As is commonly known, without switching hysteresis, electrical noise or high flow rates into the pumped container may cause the pump motor to cycle rapidly between on and off states when the fluid level is near the switching point. Such rapid cycling of the pump motor can substantially increase power consumption and shorten the life expectancy of the pump motor. It is further desirable to provide a positive (i.e., substantially bounceless) switching action because mechanical bouncing of the switch contacts may cause the pump motor to be turned on and off rapidly despite any switching hysteresis or control deadband and may cause premature wear and failure of the switch contacts.
Some conventional float assemblies provide a control deadband by coupling the float pushrod to the switch via a lost motion connection, which allows the vertical displacement of the float to change over a predetermined range of fluid levels without causing any actuation of the switch. Additionally, many of these conventional float assemblies also incorporate an electrical switch having a snap-acting or detent mechanism to provide a positive switching action that eliminates or minimizes contact bounce.
In one known configuration illustrated in FIG. 1, a conventional float 10 follows the level of a fluid within a tank 12. A pushrod 14 extends coaxially from the float 10 and is coupled to the float 10 so that the pushrod 14 follows the vertical displacement of the float 10. The pushrod 14 passes freely through an opening (not shown) in a lever arm 16 which is coupled to a detent switch 18. The pushrod 14 includes an upper pushnut 20 and a lower pushnut 22 that define a control deadband therebetween. This control deadband allows the pushrod 14 to move vertically through the lever arm 16 a predetermined distance without actuating the lever arm 16 or the detent switch 18.
At a low fluid level 24, the pushrod 14 is retracted into the tank 12 so that the upper pushnut 20 pulls the lever arm 16 downward to cause the detent switch 18 to be in one of two switching states. Similarly, at a high fluid level 26, the pushrod extends out of the tank 12 so that the lower pushnut 22 pushes the lever arm 16 upward to cause the detent switch 18 to be in the other one of the two switching states.
While the float assembly shown in FIG. 1 establishes a control deadband so that a pump motor controlled by the detent switch 18 is turned on at one fluid level and turned off at another fluid level, the structure of FIG. 1 is relatively expensive to manufacture because it requires the use of an expensive detent switch. Further, placement of the pushnuts 20 and 22 on the pushrod 14 is labor intensive and tends to be imprecise, leading to a wide variation in the minimum and maximum controlled fluid levels.